Wave

Wave, in physics, energy that travels in rhythmical motions. Waves may travel on a substance (waves on water), through a substance (the waves of an earthquake through the earth), or in a space devoid of matter (radio waves through space). The top of a wave is the crest, the bottom of a wave is the trough. Wavelength refers to the distance between 2 consecutive crests. There are 3 kinds of waves: transverse, standing, and longitudinal. In transverse waves the energy flows in a steady forward direction and causes the medium through which it travels to move up and down, like water waves. Standing waves are created by 2 identical waves moving in opposite directions, creating a series of loops. Longitudinal waves travel in a forward direction in a series of short back-and-forth motions, like the coils of a spring.

See also: Physics.